As a measurement device that measures switching contact wear, which is one of condition parameters of a circuit breaker, there has been, for example, a device that measures, by detecting using optical sensors the positions of marks attached to the drive shaft connected to the drive coils of an electromagnetic actuator, and checks the amount of deviation of the marks from their original positions due to wear of the contacts (for example, refer to Patent Document 1).
Patent Document 1: GB Patent Application Publication No. 2350724A (lines 15-20 on page 5 and FIG. 4)